Although the receptive field properties of mammalian ganglion cells are quite pertinent to visual function, little is known concerning the presynaptic pathways which underlie the properties of these cells. This project proposes to examine the influence of horizontal cells upon the receptive field properties of ganglion cells the rabbit retina by the use of intracellular and extracellular recording techniques and by pharmacological manipulations. In particular, horizontal cells will be artificially polarized by intracellular current injections and the resultant effects upon visually-evoked ganglion cell activity studied. These experiments will determine whether horizontal cells mediate the surround responses of ganglion cells in the rabbit retina and whether other ganglion cell response properties, such as spatial resolution and orientation selectivity, are also influenced by horizontal cells. In addition, because different types of rabbit horizontal cells receive different proportions of rod and cone input, horizontal cell polarization of these cell types will reveal whether rod and cone pathways exert differential effects upon ganglion cell receptive field properties. Finally, the retinal pathways between horizontal and ganglion cells will be further characterized by the application of neurotransmitter blocking agents to determine whether these drugs mimic or block the effects of horizontal cell polarization upon particular properties of ganglion cells. Knowledge of neural circuitry in a mammalian retina will increase understanding of human retinal processes and enhance the diagnosis of retinal pathologies. These data from the rabbit retina will also increase understanding of the ERG and thus will enhance the diagnostic value of the ERG and improve its usefulness as a tool in ophthalmological research.